Disconnect arrangement for multi-unit printing press

ABSTRACT

A disconnect arrangement for a multi-unit press in which the transfer cylinder is supported on eccentrics which, when actuated, bodily shift the axis of the transfer cylinder a distance sufficient to separate the transfer cylinder gear teeth from the teeth of an adjacent gear in the gear train and in which the normally stationary gripper cam for the transfer cylinder grippers is shifted with the transfer cylinder such that the cam maintains concentricity with the cylinder thereby avoiding damage to the grippers as the grippers are actuated by the cam when the cylinder is disconnected.

United States Patent Giuiuzza 51 Nov. 28, 1972 [54] DISCONNECT ARRANGEIVIENT FOR 3,221,651 12/1965 Tagliasacchi ..10l 183 MULTI-UNIT PRINTING PRESS 3,516,355 6/1970 Giuiuzza 101/ 183 [72] Inventor: Pietro Giuiuzza, Milan, Italy FOREIGN PATENTS OR APPLICATIONS Assigneel (mi-cine Meccanidle 1,095,850 12/1960 Germany ..l0l/l83 8 d -p--1Mflan Italy June 197 AttomeyYount and Tarollr [21] Appl. No.: 152,852

[57] ABSTRACT F g Application i y Data A disconnect arrangement for a multi-unit press in J 8 l 71 I n which the transfer cylinder is supported on eccentrics une 9 taly 25600 N71 which, when actuated, bodily shift the axis of the 52 transfer cylinder a distance Sufficient t/o Separate the g gg gz transfer cylinder gear teeth from the teeth of an ad- [58] Field of Search 101/136, 137, 177, 183, 184, gear the gear and whlch 1 01/185 246 409 410 411 statlonary gnpper cam for the transfer cylinder gnppers is shifted with the transfer cylmder such that the cam maintains concentricity with the cylinder thereby [56] References C'ted avoiding damage to the grippers as the grippers are ac- UNITED STATES PATENTS tuated by the cam when the cylinder is disconnected.

2,707,914 5/1955 Harrold ..10l/183 9 Claim, 8 Drawing Figures PATENTED I97? 3, 703, 863

sum u 0F 5 I INVENTOR.

P/ETRO @lU/UZZA PATENTED 28 I972 3. 703, 863

I sum 5 or 5 g INVENTOR.

P/(ETRO G/l/IUZZA DISCONNECT ARRANGEMENT FOR MULTI-UNIT PRINTING PRESS This invention relates to a disconnectarrangement for multi-unit printing presses and, more particularly, to an improved arrangement for disconnecting adjacent units of a press by throwing the transfer cylinder out of meshing engagement with one of the units.

Although the invention is particularly applicable to three cylinder offset sheet fed presses having doublesized transfer cylinders, it will be appreciated that the concepts of the invention may be used in other types of presses.

When readying a printing press for printing operations or when cleaning up the press, it frequently is necessary or desirable to perform certain operations on the individual units of the press and it is highly desirable that different pressmen be able to work on different units independently of each other when performing these operations. However, it is apparent that if all the units of the press are geared together, as they are during normal printing operation, only one pressman can safely work on the press when any one of the units is being jogged or rotated unless some means is provided to disconnect each unit from the press drive.

To facilitate make-ready. and clean up, various means have been suggested for disconnecting each printing unit from the other whereby each disconnected unit can be individually rotated by an auxiliary motor. One known disconnect arrangement involves breaking meshing engagement between the transfer cylinder gear and a gear on one of the adjacent cylinders. For example, in one known type of press, the transfer cylinder gear is in meshing engagement with gears on the impression cylinders of two adjacent printing units. The transfer cylinder is supported in the frame of the press on eccentrics which, when actuated, shifts the axis of rotation of the transfer cylinder causing the associated transfer cylinder gear to move out of meshing engagement with one of the impression cylinder gears while maintaining mesh with the other impression cylinder gear. In this manner, one unit of the press may be rotated independently of the other with the transfer cylinder gear being driven with the unit with which meshing engagement has been maintained. To reconnect the units, the eccentrics supporting the transfer cylinder are actuated to throw the transfer cylinder back to its original position in mesh with the adjacent impression cylinder gear Through the use of timing gears and/or single position clutches, the proper timing of the units is re-established. An example of this type of disconnect arrangement may be found in German Patent No. DBP 1,095,850, dated June 29,1961.

One important consideration in disconnecting units of a multi-unit press relates to the grippers carried by the cylinders for transferring sheets from one unit to the next. As is well known in the art, the transfer cylinder and the impression cylinders on either side thereof are each provided with sets of grippers with one set of grippers being provided for each of the impression cylinders and, in the case of a double-size transfer cylinder, two sets of grippers for the transfer cylinder. Each set of grippers comprises a plurality of gripper fingers supported on a pivotable shaft with the shaft extending beyond one end of the cylinder. A cam follower is operatively connected to the end of the shaft with the follower being adapted to cooperate with a non-rotatable gripper cam which controls the movements of the grippers. ln disconnecting one unit from the next and individually operating the disconnected units, care must be taken to accommodate the operation of these grippers.

The arrangement disclosed in the above-mentioned German patent employs grippers which are spring biased to a normally closed position and segmental cams which cooperate with the gripper cam follower to open the grippers only when a sheet transfer is to be made. As disclosed in that patent, the segmental cams are connected to the eccentric supporting the transfer cylinder such that as the eccentric is actuated to throw the transfer cylinder out of engagement, the segmental cams are pivoted through an arc to a position wherein subsequent rotation of the transfer cylinder results in operation of the grippers at points angularly spaced from the adjacent cylinders thereby avoiding any possibility of gripper interference. Moreover, although the radial position of the segmental cams shifts relative to the transfer cylinder when the cylinder is shifted, the subsequent operation of the grippers is not adversely affected since the only function of the gripper cam is to open the grippers and any radial shifting of the cam merely results in a change in the magnitude of the opening of the grippers.

The foregoing described arrangement is wholly unsatisfactory when used with grippers of the so-called positive closed type. This type of gripper system, which is well known in the art, comprises a plurality of gripper fingers pivotally supported on a gripper shaft. A gripper dog connected to the shaft is associated with each finger. The shaft is biased by a spring in a direction tending to open the fingers and a cam follower on the end of the shaft cooperates with a stationary gripper cam to pivot the shaft in a direction to cause the gripper dogs to pivot the fingers to a closed position in engagement with the associated gripper pads.

The gripper cam in this type of system normally extends around 360 and comprises two radially offset surfaces concentric with the transfer cylinder axis corresponding to the open and closed positions of the gripper fingers. With this type of cam, there is no position to which the cam may be angularly shifted to render the operation of the grippers ineffective. Moreover, and most importantly, to support the cam on the eccentric, as suggested in the above-identified German patent, would result in radial shifting of the cam surfaces relative to the transfer cylinder axis. Since a relatively large movement is required to disconnect the transfer cylinder, for example one-half inch, it is apparent that a correspondingly large movement would be imparted to the gripper cam if supported in the manner of the German patent. As the transfer cylinder then rotates relative to the cam, the gripper cam followers, when riding on the high" portion of the cam, will pivot through a greater angle than normal with the result that the gripper dogs will exert a greater than normal closing force on the gripper fingers with the attendant possibility of damage to the gripper fingers. Moreover, supporting the cam on an eccentric may cause the cam to shift to a position where the grippers will be open when they should be closed and thus interfere with the adjacent cylinder.

It is the principal object of this invention to provide a disconnect arrangement for a multi-unit press wherein the disconnect is effected by throwing off a transfer cylinder which includes means for maintaining the operative relationship between the normally stationary gripper cam and the gripper cam followers whereby operation of the positive closed gripper fingers is the same both in the connect and disconnect position.

It is a more specific object of the invention to provide an improved disconnect arrangement for a sheet fed multi-unit printing press which includes at least one transfer cylinder having positive closed sheet gripper fingers thereon, said transfer cylinder being supported by eccentrics to shift the axis of the transfer cylinder and thereby disengage the transfer cylinder gear from the gear of an adjacent cylinder, said positive closed gripper fingers on said transfer cylinder being actuated by a non-rotatable cam having a portion concentric with the axis of the cylinder for moving the gripper fingers to a closed condition and a return spring for moving the fingers to an open condition and wherein means are provided for mounting the cam for movement in the direction of the shifting movement of said transfer cylinder to maintain the concentric portion of the cam substantially concentric with the transfer cylinder both in the connected and disconnected positions of the cylinder.

It is a still more specific object of the invention to support the gripper cam of the transfer cylinder on a cylindrical surface of one of the eccentrics supporting the transfer cylinder, which surface is concentric with the axis of the transfer cylinder shaft and wherein means are provided for retaining the cam against its adjacent side frame while allowing movement of the cam with said cylinder as the cylinder is shifted laterally.

In the preferred form of the invention, the restraining means comprises a plurality of pins which protrude from the side frame through openings in the cam with the pins being provided with gibs to permit shifting of the cam only in a plane parallel to the plane of the side frame. One of the pins is cylindrical and is provided with a pivotal parallel sided guide block which is received in a correspondingly dimensioned slot in the cam. The slot extends in the general direction of the shifting movement of the cam to allow the cam to shift while retaining the general angular position of the cam with respect to the side frame.

These objects, features and advantages of the invention, as well as others, will be more apparent upon a complete reading of the following description which, together with the attached drawings, discloses but the preferred form of the invention.

Referring now to the drawing wherein like reference numerals indicate like parts in the various views:

FIG. 1 is a fragmentary schematic side elevational view of a multi-unit sheet fed printing press constructed in accordance with the principles of this invention.

FIG. 2 is a schematic side elevational view illustrating the connect and disconnect positions to which the transfer cylinder may be shifted.

FIG. 3 is a elevational view showing the relationship of the gripper cam to the transfer cylinder.

FIG. 4 is a fragmentary side elevational view of the gripper assembly.

FIG. 5 is a perspective view of a conventional positive closed gripper.

FIG. 6 is a sectional view showing the support of the gripper cam on the side frame and on the eccentric support for the transfer cylinder.

FIG. 7 is a schematic view showing the drive gears and timing gears in one of the printing units.

FIG. 8 is a view taken along line VIIIVIII of FIG. 7.

Referring now more in detail to the drawings wherein the showings are for the purpose of illustrating a preferred embodiment only and not for the purposes of limiting same, there is illustrated in FIG. 1 a portion of a muIti-color sheet fed offset lithographic press generally indicated by the reference numeral 10 and which comprises a plurality of printing units, two of the printing units 11, 12 being shown. As is well understood in the art, each of the printing units includes an impression cylinder 14, and cylinder means comprising a blanket cylinder 16 and a plate cylinder 18 which carries the image to be printed. Each unit also includes a dampening mechanism and an inking mechanism, not shown, both of which are conventional in the art and function in conventional manner to supply dampening fluid and ink to the plate cylinders.

A feeding mechanism, not shown, supplies sheets to the impression cylinder 14 of the first printing unit. The sheet is then carried through the printing nip of the first printing unit by the impression cylinder 14 and is trans ferred to a first double-sized transfer cylinder 20 which carries the sheet to the impression cylinder of the second printing unit 12, and in this manner the sheet passes through each of the printing units and is ultimately delivered to a delivery mechanism, also not shown.

The cylinders of the press are intergeared in a conventional manner with the transfer cylinder having gears which mesh with gears on the adjacent impression cylinders and the impression cylinder gears drive gears on their respective blanket cylinders which, in turn, drive gears on the associated plate cylinders. FIG. 2 illustrates the drive arrangement between one of the transfer cylinders 20 and the two adjacent impression cylinders 14 and includes a gear 22 secured for rotation to the transfer cylinder shaft 24. That gear meshes with an impression cylinder gear 26 secured to the impression cylinder shaft 28 of the first printing ,unit and with the impression cylinder gear 30 secured to the impression cylinder shaft 32 of the second printing unit 12. As shown in FIG. 2, the transfer cylinder gear 22 has been thrown out of mesh with the impression cylinder gear 30 by a mechanism to be described hereinafter but it is .to be appreciated that in the connected position, the

transfer cylinder gear is in meshing engagement with both of gears 26, 30 and thereby transmits drive from the main drive motor from the first printing unit 11 to the second printing unit 12.

To transfer the sheets from the first printing unit 11 to the second printing unit 12, the press employs a conventional positive closed gripper system on each of the impression cylinders 14 and the transfer cylinder 20. This gripper system is best illustrated in FIGS. 4 and 5 wherein one of the grippers for the transfer cylinder is illustrated. As shown, the gripper system comprises a gripper shaft 40 which extends longitudinally of the associated cylinder and is disposed in a gap in the periphery of the cylinder. The gripper shaft 40 is pivotally supported on the cylinder with one. end of the shaft extending beyond the end of the cylinder. Axially spaced along the gripper shaft 40 are a plurality of gripper fingers, one such gripper finger being shown in FIG. 5. As illustrated in that Figure, the gripper finger 42 includes a base portion 44 having a cylindrical bore therethrough to permit assembly of the gripper finger over the gripper shaft. The base 44 is bifurcated with a gripper dog 46 received in the bifurcation. This gripper dog is secured to the shaft 40 for pivoting movement with that shaft and includes a pair of opposed dog surfaces 48, 50. The gripper dog surface 48 is adapted to provide an abutment for one end of a light coil spring 52 with the other end of the coil spring abutting against the gripper finger 42. The gripper dog surface 50 is adapted to engage a corresponding mating surface on the gripper finger 42. A gripper pad 54 is associated with each of the fingers 42.

The end of the gripper shaft extending beyond the end of the cylinder supports a suitable cam follower arrangement which includes a lever 56 secured to the shaft and a follower 57 on the end of the lever. A suitable spring 59 acts on the lever 56 to bias the follower into engagement with the peripheral surface of a cam 58 and to pivot the shaft 40 in a direction to pivot the fingers 42 to an open position.

A suitable cam configuration for actuating the grippers on the transfer cylinder is illustrated in FIG. 3. The gripper cam 58 includes a pair of cam surfaces, 60, 61 which comprise low and high portions, respectively, on the cam. Each of the cam surfaces 60, 61 is concentric with the axis of rotation of the transfer cylinder 20, with surface 61 having an arcuate extent corresponding to the arcuate distance between transfer points for cylinder 20. As is well known in the art, as the gripper cam follower rides on the high portion 61 of the cam 58, the gripper dog associated with each of the gripper fingers acts to displace the gripper fingers 42 down into engagement with the gripper pads 54. As the gripper cam follower moves down onto the low portion 60 of the cam 58 under the bias of the spring 59, shaft 40 is pivoted to cause the gripper dogs to move the fingers away from the gripper pads.

The transfer cylinder 20 is supported at each end by eccentrics 70 rotatably received in cylindrical bores 72 in both side frames 74. The eccentrics 70 are adapted to be rotated by an actuating mechanism which includes a pair of toggle links 76, 77 with the link 77 being connected to the eccentric and the link 76 connected to a segmental gear 78. The segmental gear 78 meshes with a worm gear 80 which is adapted to be rotated by a motor 82. As shown in FIG. 2, actuation of the motor is operative to rotate the eccentrics 70 to shift the transfer cylinder and its associated cylinder gear 22 between the dotted line position where it is in meshing engagement with gears 26, 30 and the full line position where it is in engagement only with gear 26.

A suitable timing gear arrangement illustrated in FIGS. 7 and 8 may be employed to reconnectthe individual press units in the proper timed relationship. As shown in FIG. 7, each transfer cylinder of the press unit is adapted to be driven by an auxiliary motor 86 through a suitable clutch 87 and drive train which includes a pinion 88, gear 89 secured to shaft 90 and a drive pinion 91 which meshes with the transfer cylinder gear 22. The timing gear arrangement includes a gear 92 secured for rotation to the shaft 90 and which meshes with atiming gear 93 rotatably supported on a shaft 94 secured to the frame 74. Also rotatably supported on the shaft 94 is a second timing gear 95 which is in meshing engagement with a gear 96 secured to the shaft 32 of the impression cylinder of the next adjacent unit. A single position clutch, comprising a clutch pin 98 connected to a throwout collar 99 is adapted to be received in apertures in the two gears 93 and 95 when the units are in proper timed relationship. When it is desired to disconnect one unit from the other, the pin 98 is withdrawn from the aperture in the gear 93 by a suitable throw-out lever 100, thereby permitting the transfer cylinder 20 to be driven by the auxiliary motor 86 independent of the adjacent impression cylinder. Upon reconnect, it is necessary only to realign the hole in the gear 93 with the pin 98 and reinsert the pin in that gear thereby reestablishing the proper timed relationship between the individual units.

The foregoing described arrangement thus provides a means whereby individual units of the press may be disconnected, operated independently of the other units of the press and reconnected in the proper timed relationship. However, as noted above, provision must be made to avoid damage to the grippers when the transfer cylinder is rotated in the disconnected position. To this end, this invention provides a special mounting arrangement for the gripper cam 58 so that the grippers on the transfer cylinder are operated in substantially the same manner both in the connected and disconnected positions of the cylinder. More specifically, and referring to FIG. 6, the eccentric 70 supporting the end of the transfer cylinder shaft adjacent to the gripper cam 58 is provided with an axial extension 104 which has a cylindrical external surface on which the cam 58 is supported. The cylindrical extension 104 is concentric to the axis of the transfer cylinder shaft 24.

To secure the cam 58 against rotational movement, a plurality of pins 106, supported by the side frame 74, protrude through enlarged openings 108 in the cam 58. The pins 106 are provided with gibs 110 which serve to retain the cam 58 against the side frame 74. As shown, there are two such pin and gib arrangements in combination with a third pin 112 which is also carried by the side frame and which supports a pivotal parallelsided guide block 114. This block is received in a similarly dimensioned elongated slotted opening 116. The longitudinal axis of the slot 116 extends in the general direction in which the transfer cylinder is bodily shifted to disconnect the press units.

The described support of the cam 58 provides a means for non-rotatably supporting the cam against the side frame 74, while permitting shifting movement of the cam 58 as the transfer cylinder is bodily shifted; thereby to maintain the concentricity of the cam surfaces 60, 61 with the axis of the transfer cylinder shaft 24. Thus, as the eccentrics 70 at each end of the transfer cylinder shaft 24 are rotated, the cam 58, supported on the cylindrical extension 104 is shifted with the transfer cylinder relative to the frame 74. The enlarged openings 108 permit the shifting of the cam relative to pins 106. However, the cam58 is constrained to shift in a plane parallel to the plane of the frame 74 due to the gibs 110 which maintain the cam against the frame while the cooperation of the guide block 114 in the guide slot 116 assures movement of the cam in the same generaldirection as the shifting movement of the transfer cylinder. When the transfer cylinder is returned to its original connected position, the cam 58 moves back to its original position. Hence, the concentricity of the cam surfaces'with the axis of the transfer cylinder shaft is maintained in both the connected and disconnected positions, thereby enabling the gripper mechanism to operate in substantially the same manner in both positions.

It will be appreciated that if the concentricity of the cam 58 with the transfer cylinder shaft is not maintained, the effect would be to shiftthe high portion 61 of the cam 58 radially outward. Subsequent operation of the transfer cylinder would then cause the gripper cam follower to impart greater than normal closing forces on the gripper fingers. While light springs 52 are interposed between the gripper fingers and their associated dogs, these springs are not capable of absorbing the greater movement which would be transmitted by the gripper dogs and the result would be damage to the gripper fingers. However, by this invention, such potential damage to the gripper fingers is avoided and the grippers operate in the disconnected position in the same manner as in the connected position.

While the invention has been disclosed with reference to a preferred embodiment, neither that illustrated embodiment nor the terminology employed in describing it is intended to be limiting; rather, it is intended to be limited only by the scope of the appended claims.

What is claimed is:

1. In a sheet fed printing press having a plurality of printing units each of which includes an impression cylinder having sheet gripper fingers, at least one transfer cylinder having sheet gripper fingers thereon, said transfer cylinder being located between adjacent printing units to receive sheets from one printing unit and transfer it to the next, a pair of spaced vertical side frames, each of said cylinders having a gear at one end thereof and a shaft rotatively supporting each cylinder in said side frames on parallel horizontal axes, the gears on adjacent cylinders meshing to form a gear train for transmitting power from one printing unit to the next when printing, means for uncoupling the printing units for separate and independent operations thereof comprising a pair of eccentric journals in said side frames for supporting said transfer cylinder shaft in said side frames and means for operating said eccentric journals in unison to bodily shift the axis of said transfer cylinder laterally a distance sufficient to physically separate the transfer cylinder gear teeth from the teeth of an adjacent gear of said train of gears, a first drive means for driving said gear train during printing and for driving a portion of said gear train when uncoupled, a second drive means for driving the uncoupled portion of said gear train when the transfer cylinder has been bodily shifted to separate the gear teeth, means for operating the transfer cylinder gripper fingers including a pivotal shaft supporting said fingers and extending beyond one end of the cylinder, a lever on the extending end of the shaft, and a cam follower on the end of said lever, means for operating said gripper fingers to opened and closed conditions including a non-rotatable cam having a portion concentric with the axis of the cylinder for moving the gripper fingers to closed conditions and a return spring for moving the fingers to their open condition, whereby the fingers receive sheets from one cylinder and carry them for transfer to the gripper fingers of the next cylinder, the improvement comprising: means mounting said cam for movement in the direction of bodily shifting of said transfer cylinder in response to operation of said eccentric journals to maintain the concentric portion of the cam substantially concentric with said transfer cylinder in both the coupled and uncoupled positions of said cylinder.

2. The invention set forth in claim 1 wherein said concentric portion of the cam extends from the point of receipt of a sheet by the fingers of the transfer cylinder to the point of release of a sheet to the next cylinder.

3. The invention set forth in claim 1 wherein said cam in journaled on a cylindrical surface of one of said eccentric journals, which surface is concentric with the axis of the transfer cylinder shaft at all times, and wherein means is provided for retaining the cam against its adjacent side frame while allowing movement thereof with said cylinder between its coupled and uncoupled positions.

4. The invention set forth in claim 3 wherein said retaining means comprises a plurality of pins protruding from said side frame through openings in said cam, said pins being provided with gibs to allow cam movement only in a plane parallel to the plane of said side frame.

5. The invention of claim 4 wherein one of said pins is cylindrical and is provided with a pivotal parallelsided guide block thereon and wherein said cam includes a slot closely slidingly fitting the sides of said guide block, said slot extending in the general direction of bodily shifting of said cam to allow said shifting while retaining the general angular position of said cam with respect to said side frame in both the coupled and uncoupled positions of said transfer cylinder.

6. The invention of claim 1 including a set of timing gears, one of which is operatively connected with said transfer cylinder gear and another of which is operatively connected with the gear from which the transfer cylinder gear is separated, said timing gears including a pair of side-by-side gears on a common'axis and a oneposition clutch having mating parts on said side-by-side timing gears, and operating means for said clutch whereby the timing gear train may be separated during independent operation of the printing units, and the proper relationship of the separated gear teeth of the gear train may be restored by engaging the one-position clutch of the timing gear prior to recoupling the separated gears of said drive gear train.

7. The invention set forth in claim 6 wherein the timing gear in mesh with the transfer cylinder gear is so located as to maintain their gear teeth mesh when the transfer cylinder has been bodily shifted to separate the teeth of the drive gear train.

8. The invention set forth in claim 1 wherein said cam extends 360 about the axis of said transfer cylinder, and has two radially-offset concentric portions corresponding respectively to the open and closed conditions of the transfer cylinder gripper fingers.

9. The invention set forth in claim 8 wherein the concentric cam portion for closing the gripper fingers is of a larger radial dimension than the other concentric cam portion, and is located on the side of the axis of the transfer cylinder toward which the cylinder shifts when being uncoupled. 

1. In a sheet fed printing press having a plurality of printing units each of which includes an impression cylinder having sheet gripper fingers, at least one transfer cylinder having sheet gripper fingers thereon, said transfer cylinder being located between adjacent printing units to receive sheets from one printing unit and transfer it to the next, a pair of spaced vertical side frames, each of said cylinders having a gear at one end thereof and a shaft rotatively supporting each cylinder in said side frames on parallel horizontal axes, the gears on adjacent cylinders meshing to form a gear train for transmitting power from one printing unit to the next whEn printing, means for uncoupling the printing units for separate and independent operations thereof comprising a pair of eccentric journals in said side frames for supporting said transfer cylinder shaft in said side frames and means for operating said eccentric journals in unison to bodily shift the axis of said transfer cylinder laterally a distance sufficient to physically separate the transfer cylinder gear teeth from the teeth of an adjacent gear of said train of gears, a first drive means for driving said gear train during printing and for driving a portion of said gear train when uncoupled, a second drive means for driving the uncoupled portion of said gear train when the transfer cylinder has been bodily shifted to separate the gear teeth, means for operating the transfer cylinder gripper fingers including a pivotal shaft supporting said fingers and extending beyond one end of the cylinder, a lever on the extending end of the shaft, and a cam follower on the end of said lever, means for operating said gripper fingers to opened and closed conditions including a non-rotatable cam having a portion concentric with the axis of the cylinder for moving the gripper fingers to closed conditions and a return spring for moving the fingers to their open condition, whereby the fingers receive sheets from one cylinder and carry them for transfer to the gripper fingers of the next cylinder, the improvement comprising: means mounting said cam for movement in the direction of bodily shifting of said transfer cylinder in response to operation of said eccentric journals to maintain the concentric portion of the cam substantially concentric with said transfer cylinder in both the coupled and uncoupled positions of said cylinder.
 2. The invention set forth in claim 1 wherein said concentric portion of the cam extends from the point of receipt of a sheet by the fingers of the transfer cylinder to the point of release of a sheet to the next cylinder.
 3. The invention set forth in claim 1 wherein said cam in journaled on a cylindrical surface of one of said eccentric journals, which surface is concentric with the axis of the transfer cylinder shaft at all times, and wherein means is provided for retaining the cam against its adjacent side frame while allowing movement thereof with said cylinder between its coupled and uncoupled positions.
 4. The invention set forth in claim 3 wherein said retaining means comprises a plurality of pins protruding from said side frame through openings in said cam, said pins being provided with gibs to allow cam movement only in a plane parallel to the plane of said side frame.
 5. The invention of claim 4 wherein one of said pins is cylindrical and is provided with a pivotal parallel-sided guide block thereon and wherein said cam includes a slot closely slidingly fitting the sides of said guide block, said slot extending in the general direction of bodily shifting of said cam to allow said shifting while retaining the general angular position of said cam with respect to said side frame in both the coupled and uncoupled positions of said transfer cylinder.
 6. The invention of claim 1 including a set of timing gears, one of which is operatively connected with said transfer cylinder gear and another of which is operatively connected with the gear from which the transfer cylinder gear is separated, said timing gears including a pair of side-by-side gears on a common axis and a one-position clutch having mating parts on said side-by-side timing gears, and operating means for said clutch whereby the timing gear train may be separated during independent operation of the printing units, and the proper relationship of the separated gear teeth of the gear train may be restored by engaging the one-position clutch of the timing gear prior to recoupling the separated gears of said drive gear train.
 7. The invention set forth in claim 6 wherein the timing gear in mesh with the transfer cylinder gear is so located as to maintain their gear teeth mesh when the tranSfer cylinder has been bodily shifted to separate the teeth of the drive gear train.
 8. The invention set forth in claim 1 wherein said cam extends 360* about the axis of said transfer cylinder, and has two radially-offset concentric portions corresponding respectively to the open and closed conditions of the transfer cylinder gripper fingers.
 9. The invention set forth in claim 8 wherein the concentric cam portion for closing the gripper fingers is of a larger radial dimension than the other concentric cam portion, and is located on the side of the axis of the transfer cylinder toward which the cylinder shifts when being uncoupled. 